Modern techniques for the management of recurrent cardiac arrhythmias are frequently based on the results of electrophysiology studies in a cardiac catherization laboratory. Among the most important yet difficult and time consuming aspects of these studies are the observation and accurate measurement of the timing of intracardiac electrograms. Certain preliminary observations must be made during the procedure itself (online) while more detailed analysis is done later (offline) by working through the lengthy strip chart recording with a pair of calipers and millimeter scale. The hypothesis of this proposal is that such analysis can be done more swiftly, accurately, and economically by using modern computer techniques for acquisition, measurement display and retrieval of intracardiac signals. The goal of this project is to develop a computerized system for cardiac electrophysiology studies. This will have hardware and software for: online measurement and display of electrogram timing; continuous digital storage of the signals and their timing; retrieval of sections of the record, during and after the study, with rapid display, additional analysis, and selected hard copy graphics. In Phase I the applicants demonstrated the feasibility of computer acquisition, interval analysis, display and storage of multichannel recordings from the electrophysiology laboratory. In Phase II the applicants will design, develop, and construct a prototype system and perform clinical testing and evaluation at several center.